The present invention relates generally to snubber circuits. More particularly, the present invention relates to active snubber circuits, such as those used to reduce noise generated by contact arcing.
Snubber circuits are used to reduce switching stress, such as current surges, voltage spikes and oscillations, and switching losses in an electric switching element. Snubber circuits operate to limit the rate of change of voltage across the switching element when the switch is turned off, thereby reducing turn-off power dissipation losses within the switch. A typical snubber circuit includes an absorbing circuit and a resetting circuit. A simple example of a absorbing circuit is a inductor or capacitor in series with the switching element. A wide variety of resetting circuits are known.
Passive snubbers use non-dissipative passive resetting elements. Typical passive snubbers have turn-off absorbing circuits which are not connected directly across the switching element. This type of absorbing circuit connection is generally not desirable in high-power, high-frequency applications, due to size limitations and parasitic inductance.
Active snubber circuits typically include two or more switching elements in the absorbing or resetting circuit. In most snubber circuits, a full load current is transferred to the absorbing circuit when the main switching element is turned off. It is not generally perceived as desirable to have the snubber switching element carry the full load current, since its purpose is to relieve the stress on the main switching element.
U.S. Pat. No. 5,841,268 discloses a multi-resonant soft switching snubber network for a DC-to-DC converter. The multi-resonant network includes an auxiliary switch connected to transfer energy from a parasitic capacitance of the power switching device into a resonant inductor and to achieve a zero voltage turn on of the switching device. An additional resonant path is included in the snubber network to achieve a zero voltage turn off.
U.S. Pat. No. 4,849,873 discloses an active snubber for an inverter which reduces turn off losses in the electronic switch of the inverter. The snubber includes a resistor and capacitor connected in series with each other and in parallel with the load on the power inverter and parallel, inverse connected silicon controlled rectifiers in parallel with the resistor for selectively shorting the resistor.
U.S. Pat. No. 5,814,965 to Randall discloses a reduced noise controller for a switched reluctance machine. One or more capacitor smoothing circuits, positioned in a converter for the switched reluctance machine, are used to smooth voltage transitions across a phase winding.
U.S. Pat. No. 5,828,559 to Chen discloses a soft switching device for an electric power switching application. The device includes a soft switching active snubber having a capacitor, a rectifier, and a soft switching active reset circuit for actively resetting the capacitor.
U.S. Pat. No. 5,414,613 to Chen discloses a soft switching active snubber for a power conversion circuit operated in a discontinuous mode. The circuit includes a snubber capacitor, an isolation diode, and an active reset circuit. The snubber capacitor is connected to the output of the isolation diode, both of which are connected across a main switch of the power conversion circuit. The active reset circuit is responsive to a reset signal for active resetting of the snubber capacitor within the normal boost cycle of the power conversion circuit.
It would be desirable for an active snubber circuit to be smaller than conventional snubber circuits, to offer a controllable dV/dt, to offer a relatively wide load current range, and be resistant to vibration.
The present invention overcomes the above-noted problems, and achieves additional advantages, by providing for an active snubber circuit that is small in size, has a controllable dV/dt feature, is rugged, and is resistant to vibration damage. According to exemplary embodiments, an active snubber circuit includes a power device such as a field effect transistor, a resistor and a diode connected between the gate of the power device and one terminal, a capacitor connected between the gate of the power device and the other terminal. The components are preferably implemented using surface mount technology, resulting in a low profile device, and the resistance of the surface mount resistor can be varied to adjust the dV/dt of the snubber circuit.
Alternative embodiments allow the snubber circuit to be used to eliminate noise generated by contact arcing, or in power conversion applications such as for motor insulation protection, or as a clamping circuit which dissipates arc energy in the power device while clamping the voltage at a specified level, or as a snubber with active dV/dt control.